Stretcher for stretch forming sheet and plate stock

ABSTRACT

The stretcher comprises a frame with two stretch units mounted thereon for adjustment toward and away from each other for accommodating therebetween selected lengths of sheet or plate stock to be stretched or stretch formed. A male die is supported between the units when stretch forming is to be effected. Each unit comprises a linkage rockable by power means about a horizontal pivot extending transversely of the stock and tensioning dimension, and carries a stock gripping head. Rocking of the linkages causes the heads to swing about their pivots in directions away from each other for stretching the stock and toward the frame for laying the stock onto the die. The stretcher is characterized in that the horizontal pivot is adjustable along a path extending generally upwardly and downwardly normal to the plane of the stock, and the units can be latched securely in adjusted positions along the frame. With these adjustments, a preselected exact amount of total stretch can be imparted to the stock.

United States Patent [72] lnvcntor Robert A. Mackenzie [54] STRETCHER FOR STRETCH FORMING SHEET AND PLATE STOCK 7 Claims, 6 Drawing Figs.

[52] U.S.Cl

[56] 1 References Cited UNlTED STATES PATENTS 12/1965 Dolney 1/1963 Wheeler et a]... 10/1954 Green.......... 10/1967 7/1969 ..B2ldl1/02 Primary ExaminerCharles W. Lanlham Assistant Examiner-Michael J. Keenan Atlorney-lohn Harrow Leonard ABSTRACT: The stretcher comprises a frame with two stretch units mounted thereon for adjustment toward and away from each other for accommodating therebetween selected lengths of sheet or plate stock to be stretched or stretch formed. A male die is supported between the units when stretch forming is to be effected.

Each unit comprises a linkage rockable by power means about a horizontal pivot extending transversely of the stock and tensioning dimension, and carries a stock gripping head.

Rocking of the linkages causes the heads to swing about their pivots in directions away from each other for stretching the stock and toward the frame for laying the stock onto the die.

The stretcher is characterized in that the horizontal pivot is adjustable along a path extending generally upwardly and downwardly normal to the plane of the stock, and the units can be latched securely in adjusted positions along the frame.

With these adjustments, a preselected exact amount of total stretch can be imparted to the stock.

PATENTEB JUL2 7 I97! SHEET 1 0F 1 INVENTOR.

PATENTEH mm m;

SHEET 3 BF 4 INVENTOR.

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PATENTEU JUL27I9T| 3; 595, 057

SHEET Q 0F 4 1W VENTOR.

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STRETCIIER FOR STRETCH FORMING SHEET AND PLATE STOCK This invention relates to a stretcher for stretch leveling and stretch forming metal sheet and plate stock, and particularly to a stretcher which is arranged for wrapping stock about a die while maintaining it under tension above its yield point and below its ultimate strength while limiting the total elongation of the stock precisely to a preselected proportion of the total length of the stock.

The stretcher of the present invention is particularly useful for stretch leveling or stretch forming the higher alloys in which the yield point and the ultimate strength are relatively close to each other, and in which the total stretch or elongation of each workpiece must be maintained within a narrowly fixed limit in order to avoid adverse affects on the physical properties of the metal thereof.

The present stretcher is designed particularly for the application of exceedingly high tonnages for stretch levelling and stretch forming large sheets or plates, such as used for the skins of the largest transport planes.

The invention is arranged for stretching stock throughout a wide range of sizes and lengths and throughout a wide range of preselected tonnages while assuring a total elongation of a precise percentage of the total length of the stock between the heads for each stretching operation.

Various specific objects and advantages will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. I is a top plan view of a stretcher embodying the principles of the present invention;

FIG. 2 is a front elevation of the stretcher illustrated in FIG. 1 part of the frame structure thereof being cut away for clearness in illustration;

FIG. 3 is a vertical cross-sectional view of the stretcher illus trated in FIG. l and is taken on line 3-3 thereof;

FIG. 4- is a fragmentary front elevation of a stretch unit showing the means for selecting the total stretch to be imposed on the stock;

FIG. 5 is a fragmentary enlarged view showing the means for adjusting the pivot of a linkage of the present stretcher; and

FIG. 6 is an enlarged fragmentary sectional view taken on line 6-6 in FIG. ll.

Referring to the drawings, the stretcher comprises a rigid base or frame ll near the ends of which are mounted stretching units 2. Each unit 2 includes a carriage 3 supported for adj ustment endwise of the frame I on wheels 4 which operate in trackways 5 at the front and rear, respectively, of the frame 1. In case of heavier tonnages, additional trackways and wheels may be provided at selected locations on the carriage.

A die space is provided on the frame 1 between the carriages 3, and is adapted to support a die D about which the stock is to be stretch formed.

The carriages 3 are adjustable along the frame 1 toward and away from the ends of the die D to selected starting positions, these positions depending upon the length of stock, the shape of the die, and the amount of elongation to be imparted to the stock.

For driving the carriages 3 along the tracks, opposite ones of the wheels 4 are fixedly mounted on a common rotatable shaft 7 which is driven by a motor 8 through a suitable chain and sprocket drive 9.

In order to anchor each carriage 3 firmly in the adjusted position to which driven, each carriage 3 is provided at its front and rear limits with vertical detents 10, respectively, each of which is driven by a suitable piston and cylinder assemblage ll, comprising a cylinder 12 connected to the carriage 3 and a piston 13 having a piston rod 14 connected to the detent 10.

The frame it is provided near its front and rear limits with endwise rows of spaced abutments 15 in black of which the detents 10 mav be disposed for latching the carriages against travel toward each other and toward the die D during the stretch forming operation.

These abutments 15 preferably are spaced apart endwise of the frame 1 a distance several inches greater than the dimension of the detent I0 endwise of the frame ll. Inasmuch as the stock which is to be formed is usually ofthe minimum of about 12 feet in length, the spacing of the carriages 3 in this manner is close enough to permit the proper stretch while allowing the carriages to be backed off, away from the die D, a certain amount after forming to permit unloading the finished part. Thus the part can be removed from the die D and the carriages 3 then immediately moved back to position wherein the detents 10 are once more against the faces of the same abutments 15 ready for loading and repeating the stretching operation.

For very extremely precise work, compression blocks of the desired thickness can be interposed between each detent l0 and the abutment I5 with which it is to cooperate.

Mounted on each carriage 3 are parallel rocker links 16, arranged one at each side of the carriage. At one of its ends, each link is connected to its carriage 3 by a pivot 17, for rocking about the axis thereof. Near its opposite end, each link 16 is connected by suitable trunnions 18 to a piston and cylinder assemblage 19.

Each assemblage 19 comprises a cylinder 20 in which is a reciprocable double end piston 21 having a double rod 22. One end of the rod 22 is connected by a suitable pivot 23 to the carriage 3 so that, when the pistons are moved downwardly in their cylinders, the links 16 are swung upwardly to loading position, as indicated by the dotted line 16a in FIG. 4, and when the piston is forced upwardly in the cylinder, the link 16 is moved in the stretching direction to the final position shown in solid lines in FIG. 4.

Additional links 16 may be provided at points between the links l6 illustrated, if desired, depending upon the tonnages and strength required.

A rigid beam 2% is pivotally mounted at its ends in the links 16 for rocking about a horizontal axis spaced between the axes of the pivots l7 and trunnions l8 by trunnions 25. A stretch head 26 is connected to the beam 2 ll for rocking about a horizontal axis extending generally endwise of the frame l, by means of a collar 2'7 and pivot 28. The head 26 may be lineal or articulated, as illustrated.

As shown, the head comprises a plurality of jaw segments 30 which are pivotally connected together by pivots 31. The middle segment 30 is fixedly connected to the pivot 28 for rocking about the axes thereof. The segments 30 adjacent the middle segment are supported thereby, and the outer segments are supported by the ones adjacent to them, respectively.

Piston and cylinder assemblages 32 are provided for rocking each of the segments 30, except the middle segment, about its respective pivot 31 relative to the segments adjacent to it so as to provide a head having a throat ranging from lineal to approximately the general transverse curvature of the stock desired in the final product. Suitable adjustable stops 33 are provided for limiting the movement of the segments 30 so that they can be moved from a straight line position for receiving a planar margin of the sheet, to a curvilinear position while gripping the margin, by operating the piston and cylinder assemblage 32. One such assemblage 32 :is connected between each two segments 30, the cylinder being pivotally mounted on one segment and the piston rod pivotally connected to the adjacent segment.

Each segment has a pair of gripping jaws 35 defining a throat extending from the axis of one of its pivots 31 to the axis of its other pivot 3ll. Jaw closing cylinders 36 are provided on the segments 30, respectively, and are operable to cause the jaws 35 to grip the margin of the stock for applying tension thereto.

Thus the segments can be placed in alignment and the planar margin of the sheet or plate stock inserted, the cylinders 36 operated to grip the margins, and the assemblages 32 operated to arch the stock transversely so that it is convex upwardly in cross section.

The amount of stretch to be given each sheet from a given starting position of the carriages 2 must be accurately controlled and for this purpose each of the pivots 17 is mounted in its carriage for movement to different adjusted positions in a path which is at least predominantly upright.

ln the form illustrated, the pivots 17 are mounted in rigid slides 40 which slide in vertical lineal slideways 41, respectively, in side frame members 42 of the carriages 3. As best illustrated in FlG. 5,,each slide 40 is raised and lowered by a conventional worm gear screw jack 43 having an upright screw 43a and driven by a reversible electric motor 44. The motors 44 on the same carriage 3 preferably are tied together electrically by a conventional tie motor or other electronic control, so they operate in synchronism with each other to assure that the slides 40 are lifted and lowered concurrently equal distances. A marker 45 is provided on the slide 40 and an indicating scale 46 is disposed alongside the slideway 41 so that the exact position of the slide is indicated. The slides 430 may be driven to adjusted position manually if desired.

By virtue of thus shifting the carriages 3 along the frame 1 and the pivots l7 vertically, to preselected positions, the total elongation imparted to the sheet can be predetermined. Thus, by vertical adjustment of the pivots 17, the stretch imposed by the links i6 is adjusted relative to the contour of the longitudinal section of the end portion of the die, with a progressive allowance for the total stretch in the stock.

The total stretch allowable is directed by the type of stock. The jaws 35 reach substantially the lower edges of the ends of the die D in the final stretched position of the jaws.

Generally, the length of the links 16 between the pivot 17 to the trunnions is such that, in the loaded position of the jaws, the stock is arched slightly upwardly so that it will remain in place without sagging before the jaws are closed, thus facilitating loading.

When the jaws are closed, the piston and cylinder assemblages 32 are operated to impart the desired curvature to the sheet transversely. This may be done after the original arch obtained during loading is removed from the sheet or it may be before the links 16 are swung downwardly. When the end margins of the stock have been gripped, the piston and cylinder assemblages 19 are then operated to swing the links 16 downwardly. This imparts to the jaws 35 the movement necessary for obtaining the preselected stretch of the sheet with allowance for the progressive stretch as the links move downwardly and for the accommodation of the jaws to a tangential relation of the stock and instantaneous point of contact of the stock and die in the direction of tensioning at all times during the stretch forming. The total amount of stretch is dietated by the type of alloy of the stock. The progressive path of the jaws relative to the die D for obtaining this total stretch and stopping at the right point while maintaining tangency to the die during the stretching operation are readily predetermined by plotting. The position of the axis of the pivots 17 for obtaining the selected paths is obtained by adjusting the units endwise of the frame l and latching them in place by the detents 10, by adjusting the pivots 17 along the guideways 40, by selection of the length of stock, and by selection of the level at which the die is supported on the frame or base 1.

The length of the link To between the axes of the pivots l7 and trunnions 25 usually can remain fixed. lf special cases so require, links of different length than those ordinarily employed may be used to obtain the exact movement of the heads required.

The matter of great importance in connection with the adjustment of the units 2 along the frame and of the pivots 17 along the guideways is the fact that the present exotic or high alloys have the yield and ultimate strength points so very close to each other that the elongation must be accurately controlled to assure that the stock is tensioned into a range above yield, but a predetermined amount below ultimate, otherwise the sheet will break or the quality will be deteriorated by over stretching. Furthermore, since the blanks used for these purposes cost several hundreds of dollars each, breakage of even a limited number of blanks will soon become economically burdensome.

As mentioned, the stretch head is rockable with the pivot 28 about the pivot axis and is rockable about a vertical axis at right angles to the pivotal axis. For these purposes the pivot 28 carries at its outer end a yoke 47 which by means of a vertical pivot 48 is connected to the center segment 30 so that the center segment supports the head 26 as a whole for rocking about both the axis of the pivot 28 and the axis of the pivot 48.

For rocking the head about the pivot 48, a piston and cylinder assemblage 49 is provided and includes a cylinder50 with a piston 51 reciprocable therein and having a rod 52. The assemblage is pivotally connected in the yoke 47 by means of a pivot 53 and the piston rod 52 is connected by a pivot 54 to an arm 55 which is rigid with the center segment 30 of the head. With this arrangement the head as a whole can be rocked about the axis of the pivot 48 by hydraulic power, or for locking the head hydraulically in rocked positions.

For rocking the head as a whole about the axis of the pivot 28, a suitable piston and cylinder assemblage 57 is provided. The assemblage includes a cylinder 59 connected in fixed position to the collar 27. A piston 60 is reciprocable in the cylinder 59 and has a rod 61 connected to the yoke 47 and arranged so that it can rock the yoke 77 about the axis of the pivot 28 through an angle of Having thus described my invention, 1 claim:

1. in a stretch unit for stretching metal sheets and plates;

a base having a die supporting area between its ends;

a stock gripping head operable to grip a margin of a sheet and to be moved along a predetermined path in a direction toward that end of the base nearer to the head for applying tension to the sheet in one edgewise dimension of the sheet when the head is so moved with stretching force;

coaxial pivot means extending, in one position, edgewise of the sheet, transversely of the length of the base;

rigid elongated link means connected at one end to said pivot means for swinging about the axis thereof;

means connecting the head to the other end of the link means and constraining the head by the link means to be swung, at a fixed distance from said axis, in opposite directions along said predetermined path of the head during swinging of the link means in said opposite directions, selectively;

said pivot and link means being located so that at least the major portion of said predetermined path' is between the axis of said pivot means and said nearer end of'the base;

adjustable support means connecting the pivot means to said base for universal adjustment of the pivot means transversely of said axis to different operating positions relative to the base while constraining the pivot means to parallelism with said one position; and

power means for swinging the link means about said axis in opposite directions, selectively, for moving the head along said path in said direction with said stretching force.

2. The structure according to claim 1 wherein:

said adjustable support means comprise a rigid carriage;

means supporting the carriage on the base for movement relative thereto generally in one path extending transversely of said axis and endwise of the base, to adjusted positions; and

means supporting the pivot means on the carriage for movement relative thereto, in a path extending transversely of said first path of said axis and toward and away from the base, to adjusted positions.

3. The structure according 0 claim 2 wherein power operable latch means are provided for latching the carriage in its said adjusted positions, selectively.

4. The structure according to claim ll wherein power operable means are provided for moving the pivot means to said adjusted positions of the pivot means, selectively, and for locking the pivot means in the selected adjusted positions, respectively.

5. The structure according to claim 2 wherein power means are provided for moving the carriage to its said adjusted positions.

power means are provided for moving the carriage to its said adjusted positions.

7. The structure according to claim 2 wherein the carriage is movable horizontally relative to the base and the pivot means is movable relative to the carriage in a path which is at least predominately upright. 

1. In a stretch unit for stretching metal sheets and plates; a base having a die supporting area between its ends; a stock gripping head operable to grip a margin of a sheet and to be moved along a predetermined path in a direction toward that end of the base nearer to the head for applying tension to the sheet in one edgewise dimension of the sheet when the head is so moved with stretching force; coaxial pivot means extending, in one position, edgewise of the sheet, transversely of the length of the base; rigid elongated link means coNnected at one end to said pivot means for swinging about the axis thereof; means connecting the head to the other end of the link means and constraining the head by the link means to be swung, at a fixed distance from said axis, in opposite directions along said predetermined path of the head during swinging of the link means in said opposite directions, selectively; said pivot and link means being located so that at least the major portion of said predetermined path is between the axis of said pivot means and said nearer end of the base; adjustable support means connecting the pivot means to said base for universal adjustment of the pivot means transversely of said axis to different operating positions relative to the base while constraining the pivot means to parallelism with said one position; and power means for swinging the link means about said axis in opposite directions, selectively, for moving the head along said path in said direction with said stretching force.
 2. The structure according to claim 1 wherein: said adjustable support means comprise a rigid carriage; means supporting the carriage on the base for movement relative thereto generally in one path extending transversely of said axis and endwise of the base, to adjusted positions; and means supporting the pivot means on the carriage for movement relative thereto, in a path extending transversely of said first path of said axis and toward and away from the base, to adjusted positions.
 3. The structure according o claim 2 wherein power operable latch means are provided for latching the carriage in its said adjusted positions, selectively.
 4. The structure according to claim 1 wherein power operable means are provided for moving the pivot means to said adjusted positions of the pivot means, selectively, and for locking the pivot means in the selected adjusted positions, respectively.
 5. The structure according to claim 2 wherein power means are provided for moving the carriage to its said adjusted positions.
 6. The structure according to claim 2 wherein power operable latch means are provided for latching the carriage in its said adjusted positions, selectively; power operable means are provided for moving the pivot means to said adjusted positions of the pivot means, selectively, and for locking the pivot means in the selected adjusted positions, respectively; and power means are provided for moving the carriage to its said adjusted positions.
 7. The structure according to claim 2 wherein the carriage is movable horizontally relative to the base and the pivot means is movable relative to the carriage in a path which is at least predominately upright. 